This program consists of light, transmission and scanning electron microscopic studies of experimental and human models of the hematopoietic and immune systems. The bone marrow is being studied to obtain insight into the stability of its vascular sinuses, the phagocytic capacity of its adventitial and endothelial layers, the organization of hematopoietic elements, the passage of cells across the vascular wall and the cytological changes in cellular maturation. The marrow is to be studied in experimental myelogenous leukemia and in the hemolytic anemia induced by phenylhydrazine. The spleen is being studied in relationship to its deep lymphatic drainage in the rat and marmot with regard to its capacity to sequester granulocytes in the marginal zone of the rat and after hemolytic anemia. Certain fundamental immunological responses are under study. They include: the splenic response in humoral antibody response to horseradish peroxidase in rabbits, the structure and change in lymphocytes (and other cells) selectively binding complement-antigen- antibody complexes; and the degranulation and histamine release by sensitized basophils treated with IgE. Lymphatic vessels in normal individuals and those with primary and secondary lymphedema will be studied and the findings correlated with lymphangiography. The effects of platelet depletion and restoration on vascular beds are being studied with particular reference to purpura and interactions of vessels and platelets. Finally, the embryology of the hematopoietic system is being pursued.